ports.js

var webdriverio = require('webdriverio');
var elm = require('./main.js');

var options = {
    desiredCapabilities: {
        browserName: 'firefox'
    }
};

var sessions = new WeakMap;
var main = elm.Main.worker();

function subscribe(program) {

  program.ports.init.subscribe(function url() {
    var client = webdriverio.remote(options).init();
    sessions.set(program, client);
    console.log('init');
  });


  program.ports.url.subscribe(function subscribe(url) {
    sessions.get(program).url(url).saveScreenshot("foo.png");
    console.log('url');
  });

  program.ports.close.subscribe(function close() {
    sessions.get(program).close();
    console.log('close');
  });
}

subscribe(main);
setTimeout(function(){ main.ports.begin.send("Begin"); }, 0)